Six-Year Results of Leucite- Reinforced Glass Ceramic Crowns

A leucite-reinforced glass ceramic material (IPS-Empress) was developed for clinical use in Zurich. A prospective clinical study of these laboratory-made all-ceramic crowns revealed encouraging result with an estimated 2-year survival rate of 95%. The aim of the present study was to determine the clinical behavior during a longer period of observation with respect to a possible fatigue fracture phenomenon reported for ceramic systems. Crowns were cemented by applying the adhesive technique. The inner crown surface was etched with hydrofluoric acid and silanized. Dentin adhesives and composite cements were utilized. The glass ceramic crowns were evaluated with mirror, probe and apical radiographs using modified US Public Health Service criteria. Crowns recorded as having neither Cnor D-criteria were defined as successful. Kaplan-Meier estimates were calculated with the lower interval of confidence at the 95% level. The patient’s drop out rate of 16.9% was relatively low. 142 crowns placed in 59 patients could be evaluated with a mean observation time (± std. dev.) of 5.1 (± 1.5) years. Of the 142 restorations, 14 were judged as failures due to fractures. This resulted in a failure rate of 9.9%. Failures were observed between 1 month and 5.5 years after cementation. The estimated 6-year survival rate for this study group (including the early group) was 89.2%. The clinical behavior of this glass ceramic crown system is judged as satisfactory after six years in function.